Investigation of Corrosion-Inhibiting Aniline Oligomer Thin Films on Iron Using Photoelectron Spectroscopy

Polyaniline (PANI) is capable of inhibiting corrosion on iron by inducing the formation of a passive oxide film. The underlying mechanism however, is unknown. We have used photoelectron emission spectromicroscopy of thin films of a model PANI oligomer to investigate its interaction with the iron oxide film covering the iron surface. The oligomer chosen was a phenyl-capped aniline tetramer (PCAT). Thin undoped films of PCAT in its leucoemeraldine form were prepared by physical vapor deposition to obtain films from ∼1 Å to over 10 nm thick. Films were investigated with a photoelectron emission microscope (PEEM) using synchrotron radiation to obtain spatially resolved valence band photoemission spectra. Analysis of PEEM results suggest that PCAT is capable of migrating several micrometers along the substrate surface and causes a decrease in substrate work function wherever present. High-resolution core level and valence band photoelectron spectroscopy using a laboratory-based photon source was used to characterize the substrate and PCAT properties near the PCAT−substrate interface. Characterization of an in situ deposited thin film reveals that the iron substrate exhibits band bending in its oxide and a decrease in work function by 0.5 eV upon adsorption of PCAT.